Modified cellulose fiber having improved curl

ABSTRACT

Disclosed is a modified cellulose fiber having improved curl characteristics. Specifically, the present invention relates to oxidized or sulfonated cellulose fibers being highly curled, wherein such curl is highly stable. The oxidized or sulfonated curled cellulose fiber may be prepared by a process comprising treating the fibers in a high energy refiner effective to provide the desired curl properties to the fiber. The modified cellulose having improved curl characteristics may be used in disposable absorbent products.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to modified cellulose fibers havingimproved curl characteristics. Specifically, the present inventionrelates to oxidized or sulfonated cellulose fibers being highly curled,wherein such curl is highly stable.

2. Description of the Related Art

The use of cellulosic fibers in products is well known. For example,cellulosic fibers may be used in paper products including bags, tags,toweling, tissue, map papers, paper patterns, napkins, poster papers,filter papers, and many other grades or uses of paper. It is also knownto use cellulosic fibers in structures or components of disposableabsorbent products such as diaper liners, diaper wrap sheets, diaperabsorbent structures, feminine napkin wrap sheets, disposable hospitalbed pads, and the like.

Many products prepared from cellulosic fibers absorb liquids orotherwise become wet during use. It is generally desirable that theproduct, upon absorbing a liquid or otherwise becoming wet during use,substantially exhibit the same properties as when the product was dry.However, many ceIlulosic fibers are not stable upon absorbing a liquidor otherwise becoming wet losing, for example, their shape, resiliency,stiffness, or strength. Thus the use of such wet-unstable cellulosicfibers in preparing a product will generally not result in a productthat exhibits the same properties when wet as when the product was dry.

It is therefore desirable to develop and produce a cellulosic fiberhaving desirable properties in both dry and wet conditions and which,thus, is suitable for use in products such as personal care absorbentproducts.

SUMMARY OF THE INVENTION

In one aspect, the present invention concerns an oxidized or sulfonatedcellulose fiber. The oxidized or sulfonated cellulose fiber ischaracterized in that it is highly curled, wherein such curls aresubstantially stable, particularly when the fiber is wet.

One embodiment of the present invention concerns an oxidized orsulfonated cellulose fiber having a curl factor greater than about 6wherein the curls are substantially stable in water.

In another aspect, the present invention concerns a process forpreparing an oxidized or sulfonated cellulose fiber, wherein theprepared cellulose fiber is highly curled and wherein such curls aresubstantially stable, particularly when the fiber is wet.

In one embodiment, the process comprises treating an oxidized orsulfonated cellulose fiber in a high energy refiner effective to providedesired curl properties to the fiber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It has now been discovered that cellulose fiber can be modified byoxidation or sulfonation and subsequently treated in a high energyrefiner to provide desired curl properties to the fiber. In accordancewith this invention, the high-energy refining of oxidized or sulfonatedcellulose fibers to an effective level of stable curls results insignificant and unexpected improvements in the properties of themodified cellulose fiber.

As used herein, an oxidized cellulose is intended to refer to acellulose chain that has any combination of aldehyde or carboxylfunctionalities present at any of or all of the carbon atoms at the 2,3, or 6 positions of cellulose or any combinations thereof.

The oxidized cellulose of the present invention can be characterized byan aldehyde content determined by copper number, with a copper numberbeneficially from about 0.05 gram to about 20 grams, suitably from about1 gram to about 15 grams, and more suitably from about 5 gram to about10 grams per 100 grams of cellulose.

As used herein, the "copper number" is meant to represent a measure ofthe reducing groups in celllose and may be used to obtain a measure ofthe aldehyde content of a cellulose. Specifically, the copper number isdefined as the number of grams of metallic copper oxide (Cu₂ O)resulting from the reduction of copper sulfate (CuSO₄) by 100 grams ofcellulose. The copper number may be determined using TAPPI standardizedtest method T 430 om-94, published by the TAPPI Press, Atlanta, Ga.,hereby incorporated herein in its entirety by reference.

The carboxyl group content of the oxidized cellulose of the presentinvention can range beneficially from about 1 milliequivalent to about100 milliequivalents, suitably from about 5 milliequivalents to about 70milliequivalents, and more suitably from about 20 milliequivalents toabout 50 milliequivalents per 100 grams of cellulose. The carboxyl groupcontent of an oxidized cellulose can be determined by reaction of theoxidized cellulose with sodium bicarbonate/sodium chloride solution andtitration with dilute hydrochloric acid. The carboxyl group content ofthe oxidized cellulose may be determined using TAPPI standardized testmethod T 237 om-93, published by the TAPPI Press, Atlanta, Ga., herebyincorporated herein in its entirety by reference.

As used herein, a sulfonated cellulose is intended to refer to a hydroxysulfonic cellulose in which both the sulfur atom of a sulfonic group anda hydroxyl group are directly attached to a carbon atom on the cellulosechain. The sulfonic group may generally be present in the acid form orin the neutralized or salt form. The hydroxy sulfonic acid functionalitycan generally be attached to any or all of the carbon atoms at the 2, 3,or 6 positions of cellulose Or any combinations thereof. The carbonatoms at the 2, 3, or 6 positions of cellulose which are not substitutedwith hydroxy sulfonic acid can generally have an aldehyde functionality,a hydroxyl functionality, a carboxyl functionality or any combinationsthereof. Representative structures of sulfonated cellulose include, butare not limited to, the following: ##STR1##

As such, the sulfonated cellulose of the present invention differs fromother sulfur containing cellulose compounds in which the sulfur atom isindirectly connected to a carbon atom on the cellulose chain as, forexample, in the case of cellulose alkyl sulfonates.

As used herein, "sulfonated cellulose" is not to be confused with"sulfonated pulp," the latter being the basis for the many varieties ofsulfite pulping processes and most of the chemithermomechanical pulpingprocesses. When sulfonating pulp, it is the lignin portion of the pulpthat is sulfonated rather than the cellulose portion. Sulfonation oflignin serves to soften the lignin and/or make it soluble under suitableconditions in the form of sulfonated lignin or a ligno-sulfonate. In thecase of chemithermomechanical pulping or its variations, the objectiveof the sulfonation has been to soften the lignin by sulfonation so thatindividual fibers can be separated from the mass with minimal damage tothe fibers. The fiber separation is accomplished by mechanical meanswith thermal assistance to the sulfonation in softening the ligninbinding individual fibers together. No attempt is made to dissolve orremove the lignin. In full chemical pulping by the sulfite process orone of its variations, the lignin is sulfonated under suitableconditions so that the lignin is dissolved and removed from the fiber asa ligno-sulfonate.

The sulfonated cellulose of the present invention can be characterizedby an average degree of sulfonic group substitution beneficially of fromabout 0.001 to about 0.2, suitably from about 0.0025 to about 0.1, andmore suitably from about 0.005 to about 0.015. As used herein, the"average degree of sulfonic group substitution" is the average moles ofsulfonic groups per mole of glucose unit in the cellulose. The maximumdegree of sulfonic group substitution that can be obtained is 3 when allhydroxyl groups in the glucose residue are oxidized to dialdehyde andsubsequently converted to sulfonates.

Cellulosic materials with a wide range of degree of polymerization aregenerally suitable for making the modified cellulose materials of thepresent invention. It is often beneficial to use cellulosic materialswith a relatively high degree of polymerization. Cellulosic materialsuitable for use in the present invention will suitably have a degree ofpolymerization greater than about 100, more suitably greater than about500, and most suitably greater than about 1000.

It has been found to be possible to produce an improvement in curlproperties in oxidized or sulfonated cellulose fiber over a wide rangeof molecular weights. While high molecular weight modified cellulosefibers are generally preferred, it is important that improvements incurl properties in low molecular weight modified cellulose fibers canalso be achieved. For reasons of efficiency, it is often desirable toform an aqueous dispersion comprising the highest concentration ofmodified cellulose fiber possible while still being able to effectivelywork with the aqueous dispersion.

The oxidized or sulfonated cellulose fiber of the present invention hasbeen found to exhibit a desired amount of fiber curl. As used herein,the curl of a fiber is meant to represent the fractional shortening of afiber due to kink, twists, and/or bends in the fiber and is referred toherein as the curl factor of a fiber.

The curl factor of a fiber may be measured by dispersing a sample offibers in water and transferring the fibers onto a 2 inch by 6 inchglass slide and then diluting the fibers effective to observe individualfibers. A fiber image analysis system, available from Leica CambridgeLtd., Cambridge, England, under the designation Quantimet 900 imageanalysis system, was used herein to perform the image analysismeasurements. The fibers were imaged using a scan stage and actuallength (L_(a)) and maximum projected length (L_(r)) of the fibers wasmeasured. The Curl Factor value of a fiber is obtained by calculatingthe ratio L_(a) /L_(r).

The oxidized or sulfonated cellulose fiber of the present inventionexhibits a Curl Factor value that is beneficially at least about 6, morebeneficially at least about 7, suitably at least about 8, more suitablyat least about 9, and most suitably at least about 10.

It is desired that the oxidized or sulfonated cellulose fiber of thepresent invention exhibits a Curl Factor value that is substantiallystable when the fiber is wet. Fibers that do not have wet-stable curlstend to uncurl upon wetting. The test method used for measuring the CurlFactor value herein allows the fibers to be in contact with water forabout 30 minutes before length measurements are made. Thus, the methodused for determining the Curl Factor value measured the curl of a fiberunder wet conditions and is a measure of wet curl stability.

Modified cellulose fibers exhibiting an effective Curl Factor value,such as of at least about 6, have been found, for example, to exhibitlower water retention values, higher wet and dry resiliency, andsuperior fluid intake properties as compared to modified cellulosefibers that do not exhibit an effective Curl Factor value. It has alsobeen found that the curled modified cellulose fibers of the presentinvention generally exhibit a relatively cylindrical morphology ascompared to the flat ribbon-like morphology exhibited by unmodifiedand/or uncurled cellulose fibers.

The water retention value of a fiber is intended to represent theability of a fiber to retain an absorbed liquid after being subjected toa centrifugal force for a period of time. The water retention value of afiber sample may be measured by dispersing about 0.5 gram of a fibersample into about 200 milliliters of deionized water using a Waringblender at the low setting for about 30 seconds. The slurry is thentransferred to a beaker and allowed to stand for about 16 hours. Thewater is then decanted and the fiber sample is placed in a centrifugetube and then centrifuged for about 20 minutes at about 958.5 times thegravitational force. The weight of the fiber sample after centrifuging(W₁) is measured. The fiber sample is then dried at about 105° C. forabout 2 hours. The weight of the fiber sample after drying (W₂) ismeasured. The weight of the water retained after centrifuging (W₁ -W₂)per gram of dry fiber sample (W₂) is calculated as (W₁ -W₂)/W₂ from thedata obtained, and this is expressed as the Water Retention value interms of grams of water retained per gram of dry fiber sample.

It has been found that the oxidized or sulfonated cellulose fiber of thepresent invention may be prepared by simple processes. In general, themethod of making oxidized cellulose fiber comprises the step ofoxidizing cellulose fiber with an oxidizing agent to form aldehydo orcarboxyl cellulose. In general, the method of making sulfonatedcellulose fiber comprises the steps of (a) oxidizing cellulose fiberwith an oxidizing agent to form aldehydo cellulose; and (b) sulfonatingthe oxidized cellulose with a sulfonation agent to form sulfonatedcellulose.

With regard to the oxidation reaction, there are a great many ways inwhich the chain units in cellulose can be oxidized. However, mostoxidants are unspecific in their mode of attack. Suitable oxidants forpurposes of this invention include, without limitation, sodiummetaperiodate, sodium paraperiodate, periodic acid, sodium hypochlorite,hydrogen peroxide, ozone, potassium dichromate, potassium permanganate,and sodium chlorite. Periodate ions react with the cellulose withoutdestroying its fibrous nature and result primarily in the oxidativescission of 1,2-diols to primarily produce dialdehyde oxycellulose underproper conditions. For this reason the preferred oxidizing agents arethe periodates, such as sodium metaperiodate (NalO₄).

The temperature of the oxidation reaction can suitably be from about 20°C. to about 55° C., more suitably from about 30° C. to about 50° C., andmost suitably from about 35° C. to about 40° C. At temperatures belowabout 20° C., the oxidation reaction generally proceeds too slowly to bepractical. At temperatures greater than 55° C., the oxidation ofcellulose generally proceeds too fast and causes nonuniformity of theproduct and of the cellulose.

The pH of the oxidation reaction can suitably be from about 2 to about7, more suitably from about 3 to about 6.5, and most suitably from about3 to about 5. When using sodium metapedodate, for example, it isgenerally desirable to use a pH that is between about 3 to about 4.6since at a higher pH, the sodium metaperiodate is generally converted toinsoluble paraperiodate.

If sodium metaperiodate is used as the oxidation agent, the upperconcentration of sodium metaperiodate is generally limited by itssolubility in water, which is about 14.44 grams per 100 milliliters at25° C. The maximum concentration of sodium metaperiodate which cantherefore be achieved is about 0.67M. On the other hand, atconcentrations of sodium metaperiodate below about 0.005M the rate ofreaction is generally too slow for the oxidation process to beeconomically feasible. Suitable concentrations of sodium metaperiodateare from about 0.01M to about 0.2M. At higher concentrations, althoughthe oxidation reaction will proceed faster toward the desired degree ofsubstitution, the shorter treatment time is likely to result innon-uniformity of the substitution.

With regard to the sulfonation reaction, suitable sulfonation reagentsinclude, without limitation, alkali bisulfite, such as sodium bisulfite,and a combination of sodium hydroxide and sulfur dioxide. A preferredreagent is sodium bisulfite (NaHSO₃). The concentration of sodiumbisulfite is generally not critical provided there is an excess over thestoichiometric amount required. When using sodium bisulfite as thesulfonation agent, the concentration of the sodium bisulfite is suitablyfrom about 1 to about 10 weight percent, more suitably from about 2 toabout 5 weight percent, based on the weight of the cellulose fiber.

The temperature of the sulfonation reaction is suitably from about 25°C. to about 90° C. or greater, more suitably from about 25° to about 35°C.

The pH of the sulfonation reaction is suitably from about 3 to about4.5. Although the sulfonation reaction generally proceeds faster atlower pH levels, sulfur dioxide will be lost unless the reaction iscarried out under pressure. Also, at high temperatures and acidic pH,cellulose is likely to undergo hydrolyric degradation.

A suitable method of making oxidized cellulose or sulfonated celluloseis to oxidize cellulose pulp with sodium metaperiodate at aconcentration above about 0.01M for over about one hour at about roomtemperature or above. The oxidized cellulose thus produced is thensuitably washed with water to remove any soluble reaction agents orproducts. The recovered oxidized cellulose may then be treated to impartthe desired curl to the oxidized cellulose. Alternatively, the recoveredoxidized cellulose may be suitably reacted with a greater than about 0.3percent aqueous solution of sodium bisulfite at ambient temperature orhigher for about one hour at a pH of about 4.5 to prepare a sulfonatedcellulose. The product is then washed again to remove unreacted sodiumbisulfite and any soluble reaction products. The prepared sulfonatedcellulose may be used as is in a never dried condition or partiallydried by conventional means and then treated to impart the desired curlto the sulfonated cellulose.

The method of preparation of sulfonated cellulose is shown, for example,in U.S. Pat. No. 5,522,967, by Ram Shet, issued Jun. 4, 1996, and inpending U.S. patent application Ser. No. 08/571,332, filed Dec. 13,1995, by R. Shet and R. Wallajapet, the disclosures of which are herebyincorporated herein in their entirety by reference.

The oxidation and subsequent sulfonation of cellulose can be carried outon a wide variety of raw materials including celluloses derived fromboth woody and non-woody plants, coniferous as well as deciduous trees,and by a variety of pulping processes including Kraft, Soda, a varietyof sulfite processes, and chemithermomechanical pulping. Secondary fiberobtained by recycling waste paper would also be suitable as a rawmaterial for oxidation and sulfonation.

The oxidation/sulfonation can also be carried out on any of theabove-mentioned celluloses that have been mechanically refined prior tothe oxidation/sulfonation process. When used as a pretreatment, refiningserves to bring about external and internal fibrillation of thecellulose fibers. This increases the surface area of the fibers and alsoincreases accessibility of the fibrils and cellulose chains tooxidation/sulfonation.

Cellulose is generally known to be a highly crystalline material. Thedegree of crystallinity generally depends on the source of the celluloseand its processing history. The highly-ordered crystalline structuresand the less-ordered amorphous areas generally have differentaccessibilities to oxidizing and sulfonating agents. The result of thisdifference in accessibility is that the amorphous areas and surface ofcrystallites are, in the case of reaction with an oxidizing agent,generally oxidized first and heaviest, whereas the highly crystallineareas are oxidized last and least. Swelling of the cellulose improvesthe accessibility of the oxidizing agent into the crystalline areas andfacilitates the oxidation. Any other process that would increaseaccessibility, including the use of never dried pulp, would alsogenerally be beneficial. In general, it is observed that thecrystallinity of a sulfonated cellulose decreases with an increasingdegree of sulfonic group substitution.

Cellulose suitable for use in the present invention is generally withouta substantial amount of curl prior to oxidation and/or sulfonation andsubsequent high-energy refining of the cellulose to provide the curledoxidized or sulfonated cellulose as disclosed herein. After suchtreatment processes, the oxidized or sulfonated cellulose will generallyexhibit a desired level of stable curl. It is believed that themodification of the cellulose by oxidation and/or sulfonation generallyreduces the softening temperature of the cellulose, thereby making thecellulose more conformable and pliable. Such an increase in theconformability of the modified cellulose fibers generally results in themodified cellulose fibers being favorable to the development of curl bythe application of mechanical energy. Such a change in the softeningproperties of the cellulose is thus utilized in the present invention toachieve a high curl factor in the modified cellulose by the method ofmechanical dispersing. As such, the process of the present inventiongenerally does not require the use of any additives to the cellulosefibers during the curling process or any post-treatment steps, such ascuring or similar heat-treatments, after the dispersing treatment of thefibers to achieve the desired curls. It is believed that the modifiedcellulose fibers of the present invention are capable of forming in situlinkages, such as hemiacetal, acetal, ester, or ionic, during thedispersing process and that such linkages result in the stabilization ofthe curl of the fibers.

Thus, after recovery from the oxidation and/or sulfonation process, themodified cellulose fiber is generally prepared as an aqueous pulp andthen treated with a high-energy refining process to achieve a desiredamount of fiber curl. The curling of the modified cellulose herein cangenerally be achieved by using a curlator which provides significantfiber-to-fiber contact and is capable of imparting sufficient energy tocurl the fibers. A suitable method of curling the modified fibersincludes the use of suitable shaft dispersers. A variety of shaftdispersers or equivalent mechanical devices are believed capable ofbeing suitable to obtain the desired amount of curl in the modifiedfibers of the present invention. Suitable shaft dispersers include,without limitation, nonpressurized shaft dispersers and pressurizedshaft dispersers. The consistency of the cellulose pulp subjected todispersing must generally be sufficiently high to provide effectivefiber-to-fiber contact. As such, the modified cellulose is present in apulp beneficially from about 20 to about 60 weight percent, suitablyfrom about 25 to about 55 weight percent, and more suitably from about30 to about 50 weight percent, based on the total weight of thecellulose pulp.

The temperature used during the high-energy refining process maygenerally be at any effective temperature, but is beneficially greaterthan about 25° C., suitably greater than about 40° C., more suitablygreater than about 75° C. and most suitably greater than about 100° C.In general, the upper limit for the temperature used in the process isdependent on the equipment being used and if such equipment can bepressurized since at sufficiently high temperatures the water in thecellulose pulp will boil. However, it is generally desirable to use ashigh of a temperature as is possible since the use of highertemperatures has been found to generally result in improved curl of themodified fibers as compared to the use of lower temperatures.

A typical high-energy disperser is a shaft disperser, available fromIng. S. Maule & C. S.p.A., Torino, Italy, under the designation type GRII shaft disperser. Such a device comprises an upper cylindrical housingand lower cylindrical housing which when closed encloses a rotatingshaft provided with a multiplicity of arms. The upper cylindricalhousing has three rows of knurled fingers, three inspection ports and aninlet port at one end. A drive motor for turning the shaft is providedat the inlet end along with a bearing assembly at the outlet end. Theinlet end of the rotating shaft has a screw feed section to move thepulp coming through the inlet port into the disperser. At the outlet endof the disperser is a hinged flap to adjust the outlet opening from thedisperser. The opening of the hinged flap is controlled by air bags andthis is used to adjust the back pressure in the disperser. Increasingthe back pressure in the disperser increases the degree to which thefibers are worked, leading to a higher curl factor. Steam can beinjected into the feed stream to elevate the dispersing temperature.However, because of the limitations of this disperser, it is generallynot possible to impart a sufficient amount of energy onto the modifiedfibers being treated with this disperser such that the modified fiberswill generally not exhibit the desired Curl Factor values as describedherein.

A high-energy disperser suitable for use in the present invention is amachine available from Clextral Company, Firminy Cedex, France, underthe designation Bivis high-energy disperser. The Bivis machine is a twinscrew disperser. Pulp is introduced through an inlet where it encountersa short feed screw. The feed screw transfers the pulp to a first workingzone. The working zone consists of a pair of intermeshing screws whichare enclosed in a cylindrical housing. The screws co-rotate to transportthe pulp axially through the disperser. High energy dispersing isachieved by using reverse-flighted screws which have small slotsmachined in the flights. Reverse-flighted screws are positionedperiodically along the length of both screws and serve to reverse theflow of pulp through the machine, thereby introducing back pressure.Pressure builds up in this zone and forces the pulp to flow through theslots in the reverse flights into the next forward fiighted screwsection which is at a lower pressure. This compression/expansion actionimparts a high energy to the pulp during dispersion. Steam can beinjected into the pulp to carry out high temperature dispersing. Thisdisperser has been found to generally be capable of imparting asufficient amount of energy onto the modified fibers being treated withthis disperser such that the treated modified fibers will generallyexhibit the desired Curl Factor values as described herein.

The curled modified cellulose of the present invention is suitable foruse in products requiring cellulose fibers that are substantially wetstable, such as disposable absorbent products such as personal careproducts, such as diapers, training pants, baby wipes, feminine careproducts, adult incontinent products, and medical products, such aswound dressings or surgical capes or drapes. When the modified, curledcellulose of the present invention is intended for use in disposableabsorbent products, it is typically desired that the modified cellulosehave a generally neutral or slightly acidic character.

In one embodiment of the present invention, a disposable absorbentproduct is provided, which disposable absorbent product comprises aliquid-permeable topsheet, a backsheet attached to the topsheet, and anabsorbent structure positioned between the topsheet and the backsheetwherein the absorbent structure comprises the modified cellulose of thepresent invention, wherein the modified cellulose exhibits desired curlcharacteristics.

Those skilled in the art will recognize materials suitable for use asthe topsheet and backsheet. Exemplary of materials suitable for use asthe topsheet are liquid-permeable materials, such as spunbondedpolypropylene or polyethylene having a basis weight of from about 15 toabout 25 grams per square meter. Exemplary of materials suitable for useas the backsheet are liquid-impervious materials, such as polyolefinfilms, as well as vapor-pervious materials, such as microporouspolyolefin films.

Disposable absorbent products, according to all aspects of the presentinvention, are generally subjected during use to multiple insults of abody liquid. Accordingly, the disposable absorbent products aredesirably capable of absorbing multiple insults of body liquids inquantities to which the absorbent products and structures will beexposed during use. The insults are generally separated from one anotherby a period of time.

Test Methods

Curl Factor

The Curl Factor is a test which measures the fractional shortening of afiber due to kink, twists, and/or bends in the fiber. For the purposesof this invention, a fiber's Curl Factor is measured in terms of a twodimensional plane, determined by viewing the fiber in a two dimensionalplane. To determine Curl Factor, the projected length of a fiber as thelongest dimension of a two dimensional rectangle encompassing the fiber,L_(r), and the actual length of the fiber, L_(a), are both measured. Animage analysis method may be used to measure L_(r) and L_(a). A suitableimage analysis method is described in U.S. Pat. No. 4,898,642, herebyincorporated herein in its entirety by reference. The fiber Curl Factorcan then be calculated from the following equation:

    Curl Factor=L.sub.a L.sub.r

Sulfonic Group Substitution

The sulfur content of a treated cellulose material may be determined byelemental sulfur analysis and may be expressed as a weight percent ofthe cellulose material. The sulfonic group substitution of a sulfonatedcellulose material is 0.05 times the percent sulfur content. In additionto elemental sulfur analysis, energy dispersive x-ray analysis may beused to confirm the presence of sulfur in the sulfonated cellulosematerial.

EXAMPLES

About 150 pounds of sodium metaperiodate was dissolved in about 1500gallons of water in a high-consistency pulper. The pH of the solutionwas adjusted to about 4.5 using dilute sulfuric acid. About 1500 poundsof southern softwood kraft pulp was added to the pulper. A sample of thesouthern softwood kraft pulp was evaluated and exhibited a Curl Factorof about 1.4 and a Water Retention value of about 0.94 gram/gram.

The treatment of the pulp with sodium periodate solution was performedat about 30° C. for about one hour. The pulp slurry was then diluted toabout 3 weight percent consistency with water and filtered. The filteredpulp was washed by diluting to about 3 weight percent consistency withwater, agitating the slurry for about 30 minutes and filtering the pulp.The pulp washing step was repeated 3 times and the washed pulp wasobtained at about 30 weight percent consistency.

The oxidized pulp obtained from the earlier step was then sulfonated ina second step. The pulp from the earlier step was added to about 1100gallons of water in a high consistency pulper and agitated for about 20minutes. About 75 pounds of sodium bisulfite was added to the pulpslurry and the reaction was done at about 25° C. for about one hour. Thepulp was then diluted to about 3 weight percent consistency with waterand filtered. The filtered pulp was washed by diluting to about 3 weightpercent consistency with water, agitating the slurry for about 20minutes and filtering the pulp. The pulp washing step was repeated 6times and the washed sulfonated pulp was obtained at about 30 weightpercent consistency. A sample of the sulfonated pulp was evaluated andexhibited a Curl Factor of about 2.1 and a Water Retention value ofabout 2.2 grams/gram.

A portion of the prepared sulfonated pulp, at about 30 weight percentconsistency, was fed to a high-energy disperser, available from ClextralCompany, Firminy Cedex, France, under the designation Bivis high-energydisperser. The disperser was maintained at a temperature of about 98° C.by using steam. The power input to the disperser was maintained at about6.0 horsepower-day per ton of fiber and the feed rate of the pulp wasabout 2000 pounds per hour. A sulfonated pulp at about 42 weight percentconsistency was obtained. A sample of the treated sulfonated pulp wasevaluated and exhibited a Curl Factor of about 7.8 and a Water Retentionvalue of about 0.59 gram/gram. As a comparative, a sample of theoriginal southern softwood kraft pulp was treated in the Bivishigh-energy disperser under similar conditions to those disclosed above.The treated southern softwood kraft pulp was evaluated and exhibited aCurl Factor of about 2.7 and a Water Retention value of about 0.94gram/gram.

As another comparative, a second portion of the prepared sulfonatedpulp, at about 30 weight percent consistency, was fed to a shaftdisperser, available from Ing. S. Maule & C. S.p.A., Torino, Italy,under the designation type GR II shaft disperser. The disperser wasmaintained at a temperature of about 80° C. by using steam. The powerinput to the disperser was maintained at about 2.0 horsepower-day perton of fiber and the feed rate of the pulp was about 1000 pounds perhour. About 600 pounds of sulfonated pulp at about 32 weight percentconsistency was obtained. A sample of the treated sulfonated pulp wasevaluated and exhibited a Curl Factor of about 2.9 and a Water Retentionvalue of about 0.72 gram/gram. As another comparative, a sample of theoriginal southern softwood kraft pulp was treated in the Maule disperserunder similar conditions to those disclosed above. The treated southernsoftwood kraft pulp was evaluated and exhibited a Curl Factor of about2.1 and a Water Retention value of about 0.94 gram/gram.

While the present invention has been described in terms of the specificembodiments described above, numerous equivalent changes andmodifications will be clear to those skilled in the art. Accordingly,the specific examples set forth above are not intended to limit in anymanner the scope of the invention as set forth in the appended claims.

What is claimed is:
 1. An oxidized cellulose fiber exhibiting a CurlFactor value that is at least about
 6. 2. The oxidized cellulose fiberof claim 1 wherein the oxidized cellulose fiber exhibits a Curl Factorvalue that is at least about
 7. 3. A sulfonated cellulose fiberexhibiting a Curl Factor value that is at least about
 6. 4. Thesulfonated cellulose fiber of claim 3 wherein the sulfonated cellulosefiber exhibits a Curl Factor value that is at least about
 7. 5. Aprocess for treating an oxidized cellulose fiber, the process comprisingtreating an oxidized cellulose fiber in a refining means wherein therefining means is operated at a power input of greater than about 2horsepower-day per ton of oxidized cellulose fiber, wherein the treatedoxidized cellulose fiber exhibits a Curl Factor value that is at leastabout
 6. 6. The process of claim 5 wherein the treated oxidizedcellulose fiber exhibits a Curl Factor value that is at least about 7.7. The process of claim 5 wherein the power input to the refining meansis greater than about 6 horsepower-day per ton of oxidized cellulosefiber.
 8. The process of claim 5 wherein the oxidized cellulose fiber istreated in the refining means as a pulp comprising water and betweenabout 20 to about 60 weight percent of the oxidized cellulose fiber. 9.A process for treating a sulfonated cellulose fiber, the processcomprising treating an sulfonated cellulose fiber in a refining meanswherein the refining means is operated at a power input of greater thanabout 2 horsepower-day per ton of sulfonated cellulose fiber, whereinthe treated sulfonated cellulose fiber exhibits a Curl Factor value thatis at least about
 6. 10. The process of claim 9 wherein the treatedsulfonated cellulose fiber exhibits a Curl Factor value that is at leastabout
 7. 11. The process of claim 9 wherein the power input to the shaftdisperser is greater than about 6 horsepower-day per ton of sulfonatedcellulose fiber.
 12. The process of claim 9 wherein the sulfonatedcellulose fiber is treated in the refining means as a pulp comprisingwater and between about 20 to about 60 weight percent of the sulfonatedcellulose fiber.